Process for modifying the properties of shaped structures from highly polymeric polyesters



United States Patent ()fiice 3,154,374 Patented Oct. 27, 1964 6 Claims. (31. s-rsoa.

The present application is a continuation-inpart application of our application Serial No. 798,321, filed March 10, 1959.

Shaped structures of highly polymeric linear polyesters from polybasic acids and polyhydric alcohols, especially those of polyesters containing six-membered carbocyclic compounds, for example polyesters of the polyethylene terephthalate type, for instance fibers and foils, show a very dense internal structure when subjected to stretching. This is proved for instance by the fact that such materials, under conditions usual in the application of dispersion dyestuffs in the dyeing of acetate rayon, cannot be dyed at all or only with difficulties.

A process for dyeing highly polymeric polymethyleneterephthalates with dispersion dyestuffs for acetate rayon consists in carrying out the dyeing in the presence of swelling agents, so-called carriers (cf. British patent specifications Nos. 609,943 to 609,948). The swelling agents are applied in this case in aqueous solution or dispersion. They may be added to the dyeing baths, but it is also possible to treat the highly polymeric polymethyleneterephthalates with the swelling agents in an aqueous bath immediately before dyeing. The carrier process is generally applied at elevated temperatures up to 100 C. This method of operation, above all, exhibits the drawback that due to operation in aqueous solution the compounds used have to be applied in high concentrations in order to be effective. Due to their volatility, particularly with steam, considerable losses of the active substance take place in the course of the dyeing and the preliminary treatment so that special measures have to be taken.

Since objectionable odors occur when the compounds are distilled ofl, it is necessary to operate in apparatus of special design and applying special care.

From ilritish patent specifications Nos. 697,983 to 697,986 further processes for improving the dyeing properties of fibers or fabrics of polyester fibers have become known in which the textile material is treated, before being dyed, with aqueous solutions of inorganic compounds such as zinc chloride or lithium bromide or likewise with sulfuryl chloride. The substances cause an attack of the surface and a roughening of the fiber. When applying these processes, the fibers are, however, considerably attacked hydrolytically whereby the material undergoes a loss in weight. The compounds applied must be washed out prior to dyeing by an additional washing operation. Since, when operating in this way, relatively high-concentrated solutions are applied, losses in substance continually occur, rendering the process uneconomical.

Furthermore, attempts have been made to ensure an improved dyeability by increasing the dyeing temperature to above 100 C. and by applying an elevated pressure. Since for the dyeing at an elevated temperature special apparatus are required, this process cannot be applied in every case.

It has already been proposed to improve the properties of shaped structures of highly polymeric polyesters of the polyethylene glycol terephthalate type, by applying to the shaped structures at normal or moderately elevated temperature compounds showing a swelling capacity which, under the conditions of the process, do not react with the terephthalate and which are applied as such or dissolved in organic solvents, and allowing them to penetrate into the fiber at an elevated temperature and, if necessary, in a steam atmosphere. The process can likewise be carried out by combining to a single operation the application of the aqueous substance and the thermal after-treatment by heating the shaped structures in the substance showing a swelling capacity or in its anhydrous solution. When operating according to this process temperatures up to about 200 C. have been used.

Now, we have found that it is possible to modify in a favorable manner the properties of endless filaments of highly polymeric linear polyesters of polybasic acids and polyhydric alcohols, especially those of polyesters containing six-membered carbocyclic compounds, for example of the polyethylene terephthalate type, and especially to improve their dyeability, by treating the endless filaments for a short time at a temperature in the range from about 200 C. to about 350 C., particularly in the range from 220 C. to 280 C., preferably at a temperature near the melting point of the material to be treated, by means of such chemical substances as are liquid or gaseous at the treating temperature used and as under the conditions of the process act as swelling agents without, however, reacting chemically with the polyester material. Furthermore, the above mentioned substances shall not contain groups that are suitable for reaction with the polyesters at the treating temperature, for example, carboxyl, hydroxyl, sulfonic acid, or phosphonic acid groups.

The finishing process is preferably carried out as part of or immediately after the process for manufacturing the endless filaments. The polyester materials treated according to the process of the present invention, for example the endless filaments, are further processed in usual manner in order to obtain yarns, woven fabrics, knit fabrics or the like. By the process of the present invention, the surface of the polyester material is modified so as to improve considerably its dyeability, especially with dispersion dyestuffs. The treated material can be dyed without the need for special measures being taken in the. dyeing process, for example, the addition of a carrier or dyeing at a temperature above C. under superatmospheric pressure. In addition to its enhanced absorptive capacity for a wider range of dyestuff classes, other properties of the material are also improved. The strength of the polyester material is not impaired by the treatment.

As starting materials for the process of the present invention there may be used high molecular linear polyesters of polybasic carboxylic acids and polyhydric alcohols, especially those polyesters containing six-membered carbocycles of aromatic or cycloaliphatic dicarboxylic acids, such as terephthalic acid, isophthalic acid, cyclohexane dicarboxylic acids, and dihydric aliphatic alcohols having from 2 to 6 carbon atoms, such as ethylene glycol, butane diol, propylene glycol, or diethylene glycol, for example those of the polyethylene glycol terephthalate type.

As compounds serving, under the conditions of the process, as swelling agents which do not react with the polyester material, there are concerned, above all, such compounds as do not contain reactive groups, such as carboxyl, hydroxyl, sulfonic acid, or phosphonic acid groups. As treating agents there may be particularly mentioned esters, ethers, and ketones, having at least 7 carbon atoms, preferably from 7 up to about 46 carbon atoms, in the molecule and a boiling point of above C., preferably above 250 C. There may be particularly used esters, on the one hand, of aliphatic or aromatic monoor dicarboxylic acids having from 2 to 18 carbon atoms and, on the other hand, of monoor dihydric aliphatic saturated alcohols having from 1 to 28 carbon atoms or of monoor dihydric phenols, that is of compounds with hydroxyl groups that are attached to an aromatic nucleus, especially compounds deriving from benzene or naphthalene with phenolic hydroxyl groups, such as for example, phenol, cresols, xylenes, naphthols.

Furthermore, there may be used ethers of the general formula wherein R and R represent an alkyl radical having from 4 to 18 carbon atoms or the radical of a cycloaliphatic, aromatic, aromatic-aliphatic or partially hydrogenated aromatic hydrocarbon having from 6 to 18 carbon atoms, whereby the aromatic radicals can be replaced by 1 to 4 halogen atoms. As ketones there may preferably be used compounds of the formula wherein R and R have the meanings given above. As radicals R and R there may be used for example, butyl, propyl, hexyl, octyl, nonyl, dodecyl or octadecyl radicals, furthermore the radicals deriving from benzene or alkyl benzols especially methyl and ethyl benzene, from naphthalene or alkyl naphthalenes, especially aor fl-methyl naphthalene, from tetralin, decalin, diphenyl, diphenylmethane or mono-dichlorobenzene.

In detail there may .be mentioned as preferably used treating agents, for example: sebacic acid dimethyl ester, sebacic acid diethyl ester, sebacic acid dioctyl ester, sebacic acid dilauryl ester, sebacic acid dibenzyl ester, the corresponding esters of azelaic, suberic or phthalic acid and the corresponding esters of monovalent acids, such as stearic acid, lauric acid and benzoic acid, furthermore, benzophenone, diphenyl ether, B-naphthol-ethyl ether, benzoin, diphenyl methane and ot-methyl-naphthalene.

Instead of single chemical compounds there can likewise be used mixtures of several compounds of the type as mentioned. In contradistinction to the known methods of after-treatment the period of contact with the chemical compound or mixture of compounds is extraordinarily short, which is a characteristic of the process of the invention. In the present case it is sufficient to choose an extremely short time of treatment. Due to this short period only the surface of the material is modified and the interior remains unaffected. Thus, the main body of the polymeric material is not attacked and does not suffer injury. The dyeability of the material is, however, considerably improved by the treatment according to the invention. The period required by the process depends, on one hand, on the chemical compound or mixture of compounds used and, on the other, on the reaction temperature. The period can be determined in any particular case .by short preliminary tests. In general the contact period is within the range of about 10" to 10 seconds, preferably within the range of about 10 to seconds.

The correct choice of the reaction temperature is of considerable importance for carrying out the process successfully. As in the case of the contact period, the temperature must be determined in advance. In general, a temperature near the melting point of the polyester material is chosen, but the temperature may often be above the melting point of the material. Due to the extremely short period of treatment, the polymeric material does not melt. The temperature may even be considerably higher than the melting point of the material. The upper temperature limit is the temperature at which carbonization and decomposition commence at the surface of the material. In general, a'temperature ranging from about 200 C. to 350 C., and preferably about 220 C. to 350 C., is used, and more especially a temperature from near the melting point of the polymeric material up to about 50 C. above that temperature. The process is 4 usually carried out at a temperature ranging from about 260 C. to 280 C.

For carrying out the process of the present invention, the material to be treated is passed at the speed which is to be observed at the desired period of treatment through a bath containing the treating agent and the temperature of which is kept as constant as possible at the desired temperature in the range from 200 to 350 C., to be adjusted according to the treating agent, the time of treatment and to the desired effects. It is, however, also possible to apply the treating agent to the polyester material in quantities of about 5 to 20% by weight, referred to the weight of the polyester material, at lower temperatures, for example at room temperature or at a temperature somewhat elevated, in any desired manner, for example by immersing or spraying and to perform the heat treatment at temperatures of about 200 to 350 C. subsequently. Hereby the heat can act in different manner, for example, by passing the polyester material over hot metal surfaces that are kept at corresponding temperatures, .by infrared radiation, by a treatment with correspondingly heated air or by passing the polyester material through a liquid metallic bath that had been heated to the corresponding temperature, or by combination of these methods.

It is also within the scope of the inventive conception of the present process to apply the treating agents to the fibrous material in a weaker concentration, for example, as solutions in water or in a low boiling inert organic solvent, such as a lower alcohol, for example, methanol, ethanol, or isopropanol, their low ethers, esters, or ketones, or as an aqueous emulsion, and to evaporate the solvent subsequently at temperatures up to about 110 C. and then to heat the dry fibrous material to which the treating agent is adhering to the indicated temperatures, whereby the heating process can be performed by passing the material over hot surfaces or through a hot metallic bath, or by the action of a stream of hot air, by infra-red radiation or by a combination of these methods. After the treatment, the treating agent in excess is removed from the material. If volatile compounds are used, they can be removed in simple manner by passing the material over surfaces heated to 200 to 300 C., for example, heating surfaces, irons, and the like, or by passing the treated material through a stream of air of corresponding temperature or by subjecting it to infra-red radiation or by the simultaneous application of combinations of these procedures. In such a way the treatment of endless filaments can be easily carried out by means of a throwing machine modified correspondingly, while using simultaneously a great number of twisting bobbins.

In case the treatment according to the process of the present invention is carried out in a bath of the treating agent heated to 200 to 350 C. it is also possilfle, if necessary, to treat the material directly after the treating bath, in a washing bath containing a washing solution suitable for removing the treating agent. The fiber may then be chilled in a cold water bath.

In order to attain the required short period of contact between the polyester material and the hot treating bath, one chooses a very short immersion distance, for example between 0.5 and 10 cm. The drawing-off speed is adjusted correspondingly high, so that treating times of about 10- to about 10 seconds are required. When applying the above mentioned immersion distance, the drawing-off speed is generally between about 10 and 2000 meters per minute. Usually, one will use with endless filament an immersion distance of about 0.5 to 2 cm. length at the temperature range indicated as being the preferable one, and a drawing-off speed of between about 500 and 1200 meters per minute. In certain cases it may be useful to choose for endless filaments a drawing-off speed of between 10 and meters per minute, for fiber-cables the same range of speed, but preferably between 10 and 50 meters per minute. In this case the treating temperature can be reduced so that the operation is carried out in the range of 210 to 280 C., advantageously 230 to 250 C. In this manner the strong evaporation of the treating agent heated in the treating bath almost to the boil can be reduced.

If aggregations consisting of several single filaments, for example, cables of filaments, are to be treated, it may be useful at first to impregnate the material with the treating agent and subsequently make it pass through the treating bath heated to the reaction temperature.

In the process of the invention the tension of the endless filaments during the heat treatment can be of importance since it is possible to influence the effects of the process of the present invention especially as regards the improvement of the dyeability of the material by varying the tension and by varying the temperature. By varying the tension of filaments it becomes possible at the indi cated reaction temperatures to make the fibrous material shrink in a desired degree. Generally a shrinkage of about 5 to about 35% is observed. The scope of this invention further includes adjusting a favorable final hrinkage of the filaments desired for further working up the material, by means of the shrinkage observed during the treatment as well as by a subsequent restretching of the fibrous material by the length by which it has been shrunk or by a length somewhat shorter than the length by which it has been shrunk. Therefore, final shrinkage means the possibility of shrinking of the finished filament. Under otherwise equal conditions, the effect of the treatment is the higher, the lower is the tension of filaments, i.e. the higher is the shrinkage during the period of action in the treating agent and vice versa. We have surprisingly found, that by restretching the fibrous material a further improvement of the dyeability is obtained simultaneously.

The following examples serve to illustrate the invention but they are not intended to limit it thereto:

Example 1 An endless filament made of polyethylene terephthalate and having a titer of 100/50 is passed at a draw-off speed of 400 meters per minute through a bath of sebacic acid dimethyl ester heated to 282 C. for an immersion distance of 1 cm. The entrained ester is removed by a suitable liquid-stripping device as used in a rapid spinning process and the treated filament is cooled in a bath of cold water before being spooled. On dyeing this filament by means of a blue dispersion dyestuif, a deep blue tint is obtained without application of pressure or carriers. This depth of shade is increased as compared with that obtained by a comparison dyeing carried out in the known manner with the use of a carrier.

Example 2 An endless filament made of polyethylene terephthalate and having a titer of 100/50 is thoroughly wetted by passing it for an immersion distance of cm. through a cold bath of azelaic acid dimethyl ester and the excess is pressed off by a pair of rollers. The material thus impregnated is passed at a draw-oft speed of 400 meters per minute through a bath of azelaic acid dimethyl ester heated to 230 C. The immersion distance amounts to 1 cm. As described in Example 1, the filament is then cooled in a bath of cold water and spooled. The filament so treated has a better capacity for dyeing by dispersion dyestuffs than the untreated filament both as regards depth of shade and uniformity of tint.

Example 3 An endless filament made of polyethylene terephthalate and having a titer of 100/50 is passed at a draw-01f speed of 500 meters per minute for an immersion distance of 1 cm. through a bath of benzophenone heated to 270 C. The treated material is then cooled in a bath of cold water. The capacity for dyeing by dispersion dyestuffs of the filament thus treated is considerably increased.

Example 4 An endless filament made of polyethylene terephthalate and having a titer of 50 is passed at a draw-off speed of 600 meters per minute for an immersion distance of 1 cm. through a bath of adipic acid dibenzyl ester and cooled in a bath of cold Water. After this treatment the filament can be dyed by means of dispersion dyestuffs considerably better than the untreated filament.

Example 5 An endless filament made of polyethylene terephthalate and having a titer of 100/50 is passed at a draw-off speed of 400 meters per minute for an immersion distance of 1 cm. through a bath containing ethyl-fi-naphthol ether heated to 260 C. After this treatment the filament is cooled in a bath of cold Water. It can be dyed very well by means of dispersion dyestuffs.

Example 6 A fixed filament made of polyethylene terephthalate and having a titer of 15 0/ 70, twist 350, is passed at a drawoff speed of 50 meters per minute under a tension of 2 grams over a preparation roller working at 11 revolutions per minute in a bath of terephthalic acid dibutyl ester heated to 225 C. The filament thus Well wetted is squeezed off by a pair of rollers and, in order to evaporate the remaining treating agent, passed first through a heating cabinet of 30 cm. length heated at a temperature of 320 C. and then through a heating cabinet of 1 meter length heated at a temperature of 290 C. Subsequently it is spooled. The filament thus treated can be dyed very well by means of dispersion dyestuffs. its shrinkage values are much reduced in comparison with the untreated filament. Boiling shrinkage 0.5% (untreated 0.8%), thermo-shrinkage 5.0% (untreated 8.1%).

Example 7 sion of 3 grams over a preparation roller rotating at 11 revolutions per minute in a bath of phenyl benzoate heated to 225 C. The introduction speed of the filament should amount to 55 meters per minute so that the filament may shrink by 10% during the treatment. The excess phenyl benzoate is squeezed off by means of a pair of rollers and the residue is evaporated by passing through a heating cabinet 30 cm. long, heated at 320 C. and then through a heating cabinet 1 meter long, heated to 290 C. The filament is then spooled. After this treatment the filament has a better capacity for dyeing by dispersion dyestuffs than the untreated filament. During the treatment it has been simultaneously thermofixed. Its twist is sufiiciently calmed, its boiling shrinkage still amounts to 2.5 and its thermo-shrinkage to 6.2%. A stiffening of the filament does not occur when it is treated according to the above mentioned method.

Example 8 Endless filaments made of polyethylene glycol terephthalate having a titer of 200/ 100 are passed at a draw-off speed of 25 meters per minute through a bath of benzoic acid ethyl ester maintained at 200 C. The immersion distance of the filaments is 3 cm. The filaments are then passed through a second bath of cold water. The so treated filaments absorb 70% by weight of the dyestuff used from a dyeing bath containing 3%, referred to the weight of the material to be treated, of a dyestuff of the general formula H O O NHz without carriers at 100 C. during a treating period of 60 minutes. Under equal dyeing conditions, untreated filaments absorb only 29% by weight.

The same good results are obtained when, at the working method described above, filaments made of polyethylene glycol terephthalate are passed through a bath of terephthalic acid dibutyl ester heated at 210 C.

Example 9 Endless filaments made of polyethylene glycol terephthalate having a titer of 200/ 100 are passed at a draw-ofif speed of 25 meters per minute and for an immersion distance of 3 cm. through a bath of stearylic acid methyl ester heated at 230 C. Subsequently, the filaments are passed through a bath of cold methanol.

By the treatment an evident improvement of the dyeability of the filaments is obtained.

When applying the working methods described above, there can be used with the same success instead of a bath of stearic acid dimethyl ester also a bath heated to 240 C. of lauric acid lauryl ester, or of phthalic acid dioctyl ester, or phthalic acid dimethyl ester.

Example 10 Endless filaments made of polyethylene glycol terephthalate having a titer of 200/100 are passed at a draw-oil speed of 25 meters per minute through a bath of phenylbenzoate heated at 200 C. The immersion distance is 3 cm. Subsequently, the filaments are passed through a bath of cold methanol.

When being dyed, the so treated filaments absorb 83% of the dyestuff used under the conditions described in Example 8.

When using a bath of ,B-naphthol methyl ether heated at 200 C. and applying equal working methods, equivalent results are obtained.

Example 1] Endless filaments made of polyethylene glycol terephthalate having a titer of 200/100 are passed at a draw-off speed of 50 meters per minute through a bath of phthalic acid dibutyl ester heated at 230 C. The immersion distance is 3 cm. Subsequently the filaments are passed through a bath of cold methanol for an immersion distance of cm. The so treated filaments exhibit an essentially improved dyeability as compared with the untreated filaments.

Example 12 Endless filaments made of polyethylene glycol terephthalate having a titer of 200/100 are passed at a draw-off speed of 60 meters per minute and for an immersion distance of 15 cm. through a bath of benzophenone heated at 240 C. and subsequently washed in a bath of cold methanol.

When being dyed according to the manner described in Example 8, the so treated filaments absorb 88.5% by weight of the dyestulf used.

Similar good results are obtained when using a bath of benzoin heated at 230 C. instead of the bath of benzophenone.

Example 13 Endless filaments made of polyethylene glycol terephthalate having a titer of 200/ 100 are passed at a draw-off speed of 40 meters per minute and for an immersion distance of 3 cm. through a bath of diphenyl methane heated at 230 C. and subsequently washed in a bath of cold methanol for an immersion distance of 3 cm.

When being dyed according to the dyeing process described in Example 8, the filaments absorb 65.5% of the dyestuif used.

When using a bath of oc-methyl naphthalene heated at 220 C. instead of the bath of diphenyl methane and applying the working method described above, the filaments absorb 82.5% by weight of dyestuff.

8 Example 14 Endless filaments made of polyethylene glycol terephthalate having a titer of 200/100, which are stretched but not fixed, are passed at a draw-oil speed of 25 meters per minute through a bath of sebacic acid dimethyl ester heated at 200 C. The immersion distance is 5 cm. The filaments are drawn off the bath at a speed of 20 meters per minute, so that they may shrink by 20% during the treatment in the bath. Subsequently, the filaments are passed through a bath of cold methanol for an immersion distance of 10 cm.

The so treated filaments are fixed simultaneously. After the treatment their boiling shrinkage is only 3.4%, their thermo-shrinkage 5.3% (shrinkage at 200 C.).

When being dyed according to the process described in Example 8, the filaments absorb from the dyeing bath 78% of the dyestulf used.

Similar good results are obtained when using as treating bath a bath of benzyl benzoate heated at 220 C. When being dyed according to the working method described in Example 8 the so treated filaments absorb 72.5% of the dyestufi used.

Example 15 Endless filaments made of polyethylene glycol terephthalate having a titer of 200/100 which are stretched but not fixed, are passed at a draw-off speed of 25 meters per minute and for an immersion distance of 3 cm. through a bath of diphenyl heated at 210 C. The draw-oil speed is so adjusted that the filaments may shrink by 20% during the treatment. Subsequently, the filaments are passed through a bath of cold methanol for an immersion distance of 10 cm.

When being dyed according to the dyeing process described in Example 8, the filaments absorb 72.5% by weight of the dyestuff used.

In case the treatment described above is carried out with already fixed filaments, but Without shrinkage, there is also obtained an improvement of the dyeability of the filaments. When being dyed according to the dyeing process described in Example 8, the filaments absorb 62.5% by weight of the dyestufi used.

Example 16 Endless filaments made of polyethylene glycol terephthalate having a titer of 100/ 50 which are stretched but not fixed, are passed through a cold treating-bath of 15% strength containing adipic acid dimethyl ester dissolved in methanol. The filaments are then dryed by making them circulate for several times over a rotary dryer heated at 80 C. Subsequently, they are passed over a triple roller, rotating at a speed of 50 meters per minute and through a heating cabinet heated at 250 C. passed over a second triple roller, rotating at a speed of 35 meters per minute.

During the treatment in the heating cabinet the filaments are allowed to shrink by 30%.

Subsequently, the filament are spooled.

By the treatment described above an improvement of the dyeability and a simultaneous fixation of the filaments is obtained.

Example 17 Endless filaments made of polyethylene glycol terephthalate having a titer of 50 which are stretched but not fixed are passed through a bath containing a cold aqueous emulsion of dioctylphthalate of 15% strength. The filaments are made to circulate over a rotary dryer heated at 100 C., are then passed over a triple roller, rotating at a speed of 50 meters per minute and then through a heating cabinet heated at 250 C. passed over a second triple roller, rotating at a speed of 35 meters per minute. By this treatment the filaments are allowed to shrink by 30%.

When being dyed according to the working method described in Example 8, the so treated filaments absorb 78% by weight of the dyestufi used.

When using a cold solution of 15% strength of dioctyl phthalate in methanol as treating bath and applying equal working methods, similar good results are obtained.

We claim:

1. A process for improving endless filaments made of high molecular weight linear polyesters containing sixrnembered carbocycles of polybasic acids and polyhydric alcohols, which process comprises treating said filaments during a period of from 10- second to 10 seconds at a temperature of from 200 to 350 C., in the substantial absence of any dyestufli', with a swelling agent for the polyesters, said agent being chemically unreactive with the polyesters, boiling above 140 C., and being selected from the group consisting of esters of aliphatic and benzene monoand di-carboxylic acids having 6-18 carbon atoms with aliphatic alcohols having 1-12 carbon atoms, benzyl alcohol, and phenol; ethyl-fi-naphthol ether, dip'nenyl ether, benzophenone, benzoin, diphenyl methane, diphenyl, and wmethyl naphthalene, and then removing any excess swelling agent, said treating being carried out as a next step after extruding and stretching said endless filaments.

2. A process as in claim 1 wherein said treatment is carried out during a period of from 10- second to seconds at a temperature of from 260 C. to 280 C.

3. A process as in claim 1 wherein said endless filaments are passed through a heated bath of the swelling agent.

4. A process as in claim 1 wherein said swelling agent is applied to said endless filaments at a temperature below the treating temperature in an amount of from 5 to 20 percent by weight of the polyester material treated, and is then brought to the treating temperature of from 200 3. to 350 C.

5. A process for improving endless filaments made of high molecular weight linear polyesters containing sixmembered carbocycles of polybasic acids and polyhydric alcohols, which process comprises treating said filaments during a period of from 10 second to 10 seconds at a temperature of from 200 C. to 350 C., in the substantial absence of any dycstull, with sebacic acid dimethyl ester, said treating being carried out as a next step after extruding and stretching said endless filaments.

6. A process as in claim 1 wherein tension on said endless filaments during said treating is maintained such that said filaments shrink by from 5 to percent of their original length.

References (Cited in the file of this patent UNITED STATES PATENTS 2,856,638 Schulken Oct. 21, 1958 2,881,045 Mecco Apr. 7, 1959 2,901,311 Nusslein Aug. 25, 1959 2,938,811 Hermes May 31, 1960 3,034,847 Chapman May 15, 1962 

1. A PROCESS FOR IMPROVING ENDLESS FILAMENTS MADE OF HIGH MOLECULAR WEIGHT LINEAR POLYESTERS CONTAINING SIXMEMBERED CARBOCYCLES OF POLYBASIC ACIDS AND POLYHYDRIC ALCOHOLS, WHICH PROCESS COMPRISES TREATING SAID FILAMENTS DURING A PERIOD OF FROM 10-*4 SSECOND TO 10 SECONDS AT A TEMPERATURE OF FROM 200* TO 350*C., IN THE SUBSTANTIAL ABSENCE OF ANY DYESTUFF, WITH A SWELLING AGENT FOR THE POLYESTERS, SAID AGENT BEING CHEMICALLY UNREACTIVE WITH THE POLYESTERS, BOILING ABOVE 140*C., AND BEING SELECTED FROM THE GROUP CONSISTING OF ESTERS OF ALIPHATIC AND BENZENE MONO- AND DI-CARBOXYLIC ACIDS HAVING 6-18 CARBON ATOMS WITH ALIPHATIC ALCOHOLS HAVING 1-12 CARBON ATOMS, BENZYL ALCOHOL, AND PHENOL; ETHYL-B-NAPHTHOL ETHER, DIPHENYL ETHER, BENZOPHENONE, BENZOIN, DIPHENYL METHANE, DIPHENYL, AND A-METHYL NAPHTHALENE, AND THEN REMOVING ANY EXCESS SWELLING AGENT, SAID TREATING BEING CARRIED OUT AS A NEXT STEP AFTER EXTRUDING AND STRETCHING SAID ENDLESS FILAMENTS. 